Some Aspects of the Common Tern (Sterna Hirundo) Breeding Biology on the Kretuonas Lake Island

The research was carried out on the Didžioji Island, Lake Kretuonas, Aukstaitija National Park. The results obtained showed no remarkable differences between the centre and the periphery of the colony concerning predation on Common Terns (Sterna hirundo). Just embryo mortality (number of not hatched out eggs) was reliably higher in the periphery than in the centre. The most successful hatching of chicks and their survival within the first days after hatching were recorded for the tern nests with the eggs laid during the mass egg-laying season. In synchronous and asynchronous three-chick broods, survival of nestlings varied. In asynchronous broods, the last chicks grew slower due to sibling competition, percentage of their mortality being highest of all. In two- and three-chick broods, feeding intensity of each chick was, in general, similar and depended just on individual features of a certain pair and the abundance of food resources. It was due to a louder vocal stimulation that adults brought up food to...